1. Field of the Invention
The present invention relates to a recording head and an image recording device. In particular, the present invention relates to a recording head and an image recording device configured by liquid discharge ports that discharge liquid being arranged at a pitch corresponding to a resolution and plural drive elements for causing the liquid to be discharged from the liquid discharge ports in correspondence to the liquid discharge ports being arranged at a pitch corresponding to the resolution. Note that, in the present invention, “liquid” includes ink and a treatment liquid that agglomerates color materials which are included in the ink.
2. Description of the Related Art
In recent years, in image recording devices, in accompaniment with increases in the speed of image recording, there has been an increase in the print width as the result of an increase in the number of nozzles for discharging liquid disposed in a recording head used in an inkjet printer.
For example, in so-called thermal inkjet recording heads that heat the liquid and cause the liquid to be discharged from nozzles, as shown in FIG. 6A, low-resistance heaters 140 that heat the liquid and driver transistors 142 for driving the heaters 140 are disposed one apiece with respect to one nozzle. By switching the driver transistors 142 ON and OFF, a low voltage/large current is applied to the heaters 140 and the heaters 140 are driven.
In FIG. 6A, each heater 140 is connected to a line 150 to which a voltage is applied from both ends, and source terminals of the drive transistors 142 are grounded via a line 160.
In order to increase the speed of image recording without causing the image quality to deteriorate, it is necessary for the number and disposed pitch of the nozzles disposed in the recording head to correspond to the resolution of the printer. For this reason, there are instances where 600 to 800 nozzles are disposed per inch, and the miniaturization of elements configuring the recording head is progressing. Usually, each element is formed by a Large Scale Integration (LSI) process.
It is also necessary for the disposed pitch of the heaters to be the same as the disposed pitch of the nozzles, but the disposed pitch of the driver transistors is determined in accordance with the design rule of the LSI process. For this reason, it is common to make the disposed pitch of the driver transistors the same as or less than the disposed pitch of the heaters.
However, when the disposed pitch of the driver transistors is made the same as or less than the disposed pitch of the heaters, the potential differences at both ends of the heaters connected in parallel to the heater power supply exhibit a tendency to be larger towards the heaters at both ends and smaller towards the central heater, as shown in FIG. 7. This tendency becomes more pronounced as the number of heaters connected in parallel increases.
Namely, this results from wiring resistances that arise due to differences in the distances (i.e., wiring lengths) between the heaters 140 and the heater power supply. In FIG. 6B, an equivalent circuit of FIG. 6A is shown. As shown in FIG. 6B, there are wiring resistances in the conductors that electrically connect the heaters 140 to a common power supply. This is because the size of the wiring resistance is different between the heaters connected at both ends and the heater connected in the center.
The current flowing in the recording head increases as the result of an increase in the number of nozzles disposed in the recording head. For this reason, technology has been proposed to raise the withstand voltage of the entire drive system, raise the drive voltage of the recording head and lower the current. Particularly with respect to the driver transistors, it is preferable to raise the withstand voltage without raising the ON resistance.
Conventionally, as technology that can be applied in order to raise the withstand voltage without raising the ON resistance of the transistors, it has been proposed to dispose, in a MOS transistor array that drives electrothermal conversion elements connected in a matrix, channels of a type different from the source regions as voltage buffer regions so as to surround the source regions in order to raise the withstand voltage without raising the ON resistance (see Japanese Patent Application Laid-Open (JP-A) No. 03-224741).
However, in a recording head configured as described above, when voltage buffer regions are simply disposed in the source regions as proposed in JP-A No. 03-224741, the transistors become large as a result, and the conventional disposed pitch cannot be applied as is.
Also, nothing can be solved with respect to differences in the wiring resistance, and depending on the layout, the differences in the wiring resistances end up increasing.
Namely, when laying out units configured by heaters and transistors, there is usually no concern to enlarge only the disposed pitch of the drivers. Even in JP-A No. 03-224741, there is no description in regard to technology relating to the layout between the transistors and the electrothermal conversion elements in consideration of the wiring resistance.